It has long been recognized that the control of temperature and humidity conditions in certain work areas is desirable to achieve efficient operation. This is particularly so in the textile industry, for example, where large rooms typically contain a vast amount of equipment employed to process materials which are highly sensitive to ambient conditions.
One system which has been developed to control the absolute humidity in a designated area is disclosed in U.S. Pat. No. 4,312,189 which issued to Worth B. Cotton, Jr., on Jan. 26, 1982. In this patent, there is disclosed an arrangement wherein a conventional air washer is utilized in the circulation path of the air being treated. An absolute humidity sensor is positioned in the output path from the air washer, and a dry bulb thermostat is located in the area being controlled. The absolute humidity sensor operates dampers to adjustably mix fresh air with air being returned from the controlled area to an air washer. The dry bulb thermostat controls a valve in the air washer to vary the amount of water sprayed into the return air/fresh air mixture. By this arrangement, the temperature and absolute humidity conditions of the air reaching the controlled area are established.
While the system disclosed in U.S. Pat. No. 4,312,189 is a useful one, it suffers certain shortcomings. For example, the absolute humidity sensor located at the air washer's output measures absolute humidity at only a small spot. However, the absolute humidity level typically varies across the substantial surface area of the air washer. Consequently, the sensor may not provide an accurate reading of the average absolute humidity of the air discharged from the washer. Furthermore, there are many textile operations in which a large room is divided--without partitions--into zones controlled at different temperatures and relative humidities. In such a situation, some migration occurs from zone to zone which cannot be accurately compensated for by absolute humidity sensors provided at the discharges of the separate air washers which service the respective zones.